In the past, a lighting fixture including a lighting apparatus configured to turn on a light source (e.g., a discharge lamp, an incandescent lamp, and an LED) has been proposed. With respect to such the lighting fixture, when the light source comes close to the end of its life due to a long time use, a situation where the light source can not be turned on or the light source becomes hard to be turned on or the brightness of the light source is decreased occurs. Therefore, a user can easily recognize the end of life of the light source in view of the above situation. Then, the user replaces the light source.
Meanwhile, the lighting apparatus turning on the light source and a main body also have a useful life (that is, life). Long time use causes a situation, such as fatigue and/or oxidization of metal components of the lighting apparatus and/or the main body, deterioration, discoloration, and/or breakage of resin components thereof, and deterioration and/or decrease of dielectric resistance of circuit components of a lighting circuit. As mentioned in the above, both the lighting apparatus configured to turn on the light source and the main body have the life (lifetime). Even if the lighting apparatus and the main body come close to the end of life, a user is unlikely to know that the lighting apparatus and the main body come to the end of life while the light source is normally turned on. Therefore, the user often continues to use the lighting apparatus and the main body. When the user continues to use the lighting apparatus and the main body which have already come to the end of life, it is impossible to obtain a proper performance of the lighting fixture. In addition, breakage or fall of the main body is likely to occur depending on a deteriorated component thereof.
In contrast to an electric device such as the lighting fixture performing a lighting function by use of both the light source and the lighting apparatus, with respect to an electric device (e.g., TV receiver) performing a predetermined function alone, it is possible to determine that the TV receiver itself has been deteriorated when a performance of television viewing (e.g. sharpness of an image, color reproducibility and quality of sounds) is deteriorated. However, in a situation of the lighting fixture in which the lighting apparatus turns on the light source to perform the lighting function, it is difficult to distinguish the end of life of the lighting apparatus from the end of life of the light source. Therefore, it is difficult for a user to understand a degree of deterioration of the lighting apparatus. In some cases, the lighting apparatus having life of 10 years is likely to be used for at least 10 years or a few decades.
Therefore, in the past, there has been proposed a lighting fixture which includes a means configured to measure by use of a counting circuit an accumulated lighting time in which a lighting apparatus keeps turning on a light source and to determine the end of life of the lighting apparatus or a main body when the accumulated lighting time exceeds a predetermined time (see a document 1 [Japanese patent laid-open publication No. 6-333687], and a document 2 [Japanese patent laid-open publication No. 2006-23664]).
The lighting fixtures disclosed in the documents 1 and 2 indicate the end of life of the lighting apparatus or the main body when the accumulated lighting time measured by the counting circuit reaches the predetermined time. Therefore, the lighting fixture can perform a protection operation of turning off the light source prior to occurrence of abnormal heat generation of electrical components due to deterioration of the electrical components or breakage of structural components due to deterioration of the structural components at the end of life thereof. Thus, it is possible to improve safety of the lighting fixture.
For example, it is assumed that plural lighting fixtures are installed inside a tunnel. The counting circuits of the respective lighting fixtures count a clock signal generated at a predetermined oscillation frequency. Thus, counted values of the counting circuits are not so irregularly distributed. Therefore, with respect to the plural lighting fixtures installed around the same time, the accumulated lighting times of the plural lighting fixtures are likely to reach the predetermined time around the same time. Thus, the plural lighting fixtures perform the protection operation (operation of turning off the light source) simultaneously, and thereby lighting at an installation site is lost without providing prior notice. Consequently, the lighting fixture is likely to perturb people therearound and users, and safety of the lighting fixture is reduced due to a loss of lighting.
Consequently, as disclosed in a document 3 (Japanese patent laid-open publication No. 11-191168), it has been proposed to prevent the plural lighting fixture from performing the protection operation (operation of turning off the light source) simultaneously by means of irregularly distributing timings in which the plural lighting fixtures determine the end of life thereof by employing a method of using random numbers in counting circuits.
The lighting fixtures of the aforementioned documents 1 and 2 have a function of performing the protection operation at timing of the end of life, but do not have a function of performing an indication operation at timing prior to the end of life. When the method of using random numbers in counting circuits disclosed in the document 3 is applied to the lighting fixture of the document 1 or 2 in order to vary timing at which the indication operation is performed, it is possible to prevent the plural lighting fixtures from being turned off simultaneously. However, when the accumulated lighting time reaches the predetermined time, the plural lighting fixtures are turned off in sequence without providing prior notice. Therefore, the lighting fixture is still likely to perturb or discomfort people therearound and users.